Organic electroluminescent light emitting display device

ABSTRACT

In an organic electroluminescent light emitting display device comprising a plurality of pixels each of which includes an organic electroluminescent element emitting light by a current supplied thereto, a plurality of active elements including a first active element which acquires a data signal and a second active element which regulates the current supplied to the organic electroluminescent element in accordance with the data signal, and a capacitive element storing the data signal, the present invention utilizes a part of the capacitive element arranged in one of the pixels for a light shielding member which shields the plurality of active elements arranged the one of the pixels from light emitted by the organic electroluminescent element arranged therein or another pixel adjacent thereto so as to suppress image quality deterioration and smear appearing in an image display area of the organic electroluminescent light emitting display device.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a Continuation application of U.S. application No.10/376,331 filed on Mar. 3, 2003. Priority is claimed based on U.S.application No. 10/376,331 filed on Mar. 3, 2003, which claims priorityto Japanese Patent Application No. 2002-056733 filed on Mar. 4, 2002,all of which is incorporated by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an organic electroluminescent lightemitting display device which provides a region formed of an organicmaterials which emit light by an electroluminescence phenomenon, andmore particularly to a pixel structure suitable for an organicelectroluminescent light emitting display device which displays an imageby an active-matrix driving using a switching element formed on eachpixel.

2. Description of the Related Art

Expectations are growing that an organic electroluminescent lightemitting display device (hereinafter referred to as “organic EL lightemitting display device) which is driven by an active matrix method(also referred to as TFT type) will become a flat panel display of nextgeneration by replacing a liquid crystal display.

Conventional organic EL pixel constitutions and pixel circuits aredisclosed in JP-A-11-329715, JP-T-11-503868, JP-T-11-503869 and U.S.Pat. No. 6,157,356. Further, U.S. Pat. No. 5,561,440 discloses a lightshielding structure in a pixel of a display device driven by an activematrix method by taking a liquid crystal display device as an example.

SUMMARY OF THE INVENTION

While an organic EL light emitting display device has an advantage thata bright image display having high luminance can be performed, theorganic EL light emitting display device has a problem that lightemitted from a light emitting layer of an organic EL element formed oneach pixel is irradiated to a semiconductor channel of a switchingelement formed on each pixel and modulates the charge holdingcharacteristics (conductive state of the semiconductor channel) of theswitching element. In the organic EL light emitting display device whichis driven by the active matrix method, a switching element which has asemiconductor channel (hereinafter simply referred to as “channel”)formed of a polycrystalline silicon film (also referred to as “Poly-Si”)is provided to each pixel. However, the polycrystalline silicon film(Poly-Si) exhibits a large photoconductivity and hence, the apparentphotoconduction is generated in a polycrystalline silicon film inaccordance with an electric field applied thereto when light isirradiated thereto. Accordingly, with respect to the switching element(for example, thin film transistor) which includes the channel formed ofthe polycrystalline silicon film and controls a charge quantitypenetrating the channel, even when the switching element is turned off,there arises a problem that a considerable quantity of charge passesthrough the channel (so-called OFF current). For example, when a whitelight having 2000 lux (unit:lx) is irradiated to such a thin filmtransistor (also referred to as “TFT”) in a turn-off state, the OFFcurrent which is generated in the thin film transistor is sharplyincreased.

In a display device which includes an image display region on which aplurality of pixels provided with switching elements (for example, theabove-mentioned TFTs) are formed and performs image display by driving aplurality of these pixels in an active matrix method (also referred toas “TFT method”), when the above-mentioned OFF current is generated inat least one of these switching elements, the image quality of thedisplay image is degraded. With respect to an organic EL light emittingdisplay device in which an organic EL element is provided to each pixel,a light emitting portion which is included in the organic EL element isarranged close to the switching element which drives or controls theorganic EL element and hence, the switching element is exposed to lighthaving a several hundred thousands lux. Accordingly, even when aconventional light shielding structure used in the pixel region of theliquid crystal display device driven by an active matrix method(hereinafter referred to as “TFT type liquid crystal display device”) isapplied as a corresponding light shielding structure of the organic ELlight emitting display device, it is impossible to shield the pixelregion from such a strong light. Particularly, a bottom emission-typeorganic EL light emitting display device which irradiates light from theorganic EL element to a TFT substrate having a main surface on whichswitching elements are formed, the degradation of image quality of thedisplay image is liable to easily occur due to such a strong light.

It is considered that the above-mentioned unexpected problem whichoccurs due to the light emitted from the organic EL element (hereinafteralso referred to as “leaking of light”) is caused by a fact that lightwhich is generated in a certain pixel penetrates an insulation film(so-called bank layer) which separates light emitting regions (organicmaterial layers) of the organic EL light emitting display device amongpixels and is leaked to neighboring other pixel. Such leaking of lightis perceived as smear or contrast unevenness by a user of the organic ELlight emitting display device.

From a viewpoint of contrast of an image displayed on the organic ELlight emitting display device, it is very important to increase theblackness of the pixel in a non-light-emitting state. In the organic ELlight emitting display device, an influence that the leaking of lightattributed to reflection of light in the substrate or the like gives tothe black display is larger than the corresponding influence in theliquid crystal display device. Accordingly, the high luminance of thepixel in the white display state is also cancelled by the leaking oflight which is generated when the pixel is in the black display stateand hence, the contrast of the display image is still held at a lowlevel. As a result, the image quality of the display image inevitablybecomes inferior to the image quality of the display image of the liquidcrystal display device.

Further, with respect to the organic EL light emitting display device,the enlargement of the light emitting region in each pixel is alsoimportant. In manufacturing steps of the organic EL light emittingdisplay device, when an organic electroluminescent material of i.e.polymeric series is supplied to each pixel in a solution state, it isnecessary to form an opening having a depth which is sufficient fortemporarily storing the solution made of the organic EL material in theabove-mentioned bank. Accordingly, with respect to the bottomemission-type organic EL light emitting display device which irradiateslight to the TFT substrate side, the reduction of the light emittingregion caused by narrowing the opening on the bank at the TFT substrateside must be taken into account. Accordingly, a region which isallocated to the formation of the opening on an upper surface of thebank cannot be made extremely small. On the other hand, a pixel circuitwhich controls the organic EL element formed on the pixel is also formedon each pixel. Accordingly, it is necessary to ensure a region which isserved for a switching element and a capacitance element included in thepixel circuit at each pixel. Under such circumstances, it is necessaryto skillfully arrange the above-mentioned two regions on a plane insideeach pixel.

On the other hand, another kind of organic EL material having molecularweight thereof lower than that of the above-mentioned organic ELmaterial of the polymeric series is also able to be utilized for formingthe organic EL element. The another kind of organic EL material is alsocalled as an organic EL material with low molecular weight because themolecular weight thereof is so low that this kind of organic EL materialcan be supplied to each pixel (having the organic EL element) in asublimed state. Therefore, an application of the organic EL materialwith low molecular weight to forming the pixel permits an opening in theabove-mentioned bank to be formed shallower than that for the organic ELmaterial of the polymeric series. However, also in the organic EL lightemitting display device having organic EL elements made of organic ELmaterial with low molecular weight, it is necessary to arrange the lightemitting region and the pixel circuit region on a plane at each pixel asdescribed above.

The present invention has been made to solve the above-mentioneddrawbacks under such circumstances. As typical constitutions of theorganic EL light emitting display device to which the present inventionis applied, followings are considered.

(1) A first example of an organic electroluminescent light emittingdisplay device according to the present invention comprises a substratehaving a principal surface, a plurality of pixels arrangedtwo-dimensionally on the principal surface of the substrate, a pluralityof scanning signal lines juxtaposed along a first direction on theprincipal surface of the substrate, a plurality of data signal linesjuxtaposed along a second direction transverse to the first direction onthe principal surface of the substrate, and a plurality of currentsupply lines arranged on the principal surface of the substrate. Each ofthe plurality of pixels has a plurality of active elements including afirst active element which acquires a data signal transmitted by one ofthe plurality of data signal lines in response to a voltage signal ofone of the plurality of scanning signal lines and a second activeelement which regulates a current supplied from one of the plurality ofcurrent supply lines in accordance with the data signal, a data storingelement storing the data signal acquired by the first active element,and an organic electroluminescent element emitting light by the currentwhich is regulated by the second active element and supplied to organicelectroluminescent element. At least one of the plurality of pixelsincludes a light shielding member which shields the plurality of activeelements arranged therein or in another of the plurality of pixelsadjacent thereto from light emitted by the organic electroluminescentelement arranged therein.

(2) A second example of the organic electroluminescent light emittingdisplay device according to the present invention comprises a substratehaving a principal surface, a plurality of scanning signal linesjuxtaposed along a first direction on the principal surface of thesubstrate, a plurality of data signal lines juxtaposed along a seconddirection transverse to the first direction on the principal surface ofthe substrate, a plurality of current supply lines arranged on theprincipal surface of the substrate, and a plurality of pixels arrangedtwo-dimensionally on the principal surface of the substrate. Each of theplurality of pixels has a plurality of active elements including a firstactive element which acquires a data signal transmitted by one of theplurality of data signal lines in response to a voltage signal of one ofthe plurality of scanning signal lines and a second active element whichregulates a current supplied from one of the plurality of current supplylines in accordance with the data signal, a data storing element storingthe data signal acquired by the first active element, and an organicelectroluminescent element emitting light by the current which isregulated by the second active element and supplied to organicelectroluminescent element. Moreover, the second example of the organicelectroluminescent light emitting display device also comprises a firstlight shielding member arranged at a position where the first lightshielding member obstructs light from the organic electroluminescentelement arranged the one of the plurality of pixels to the plurality ofactive elements arranged at the pixel or another of the plurality ofpixels adjacent to the one of the plurality of pixels, and a secondlight shielding member arranged at a boundary between a pair of theplurality of pixels adjacent to one another and blocking off opticalleakage between the pair of the plurality of pixels at the boundary.

Switching elements like thin film transistors each of which has achannel layer formed of a poly-crystal or a pseudo-single crystal of asemiconductor material are provided for instance as the plurality ofactive elements of each of the aforementioned first and second examplesof the organic electroluminescent light emitting display deviceaccording to the present invention. An example of the organicelectroluminescent element provided for each of the first and secondexamples of the organic electroluminescent light emitting display deviceincludes a transparent electrode receiving the current supplied from thesecond active element, an insulating film (called “Bank”, also) formedon the transparent electrode and having an opening which exposes a partof an upper surface of the transparent electrode, and an organicmaterial layer formed on the part of the upper surface of thetransparent electrode. The insulating film is formed e.g. of adark-colored material (a black-colored material), or an inorganicmaterial. The insulating film may be formed of a material of poly-imideseries, also. Moreover, the opening of the insulating film may be formedto be tapered toward the upper surface of the transparent electrode inits cross section.

More concrete constitutional examples of the aforementioned firstexample of the organic electroluminescent light emitting display deviceaccording to the present invention will be described as follows,respectively.

(1a) When the organic electroluminescent element includes a transparentelectrode receiving the current supplied from the second active element,an insulating film formed on the transparent electrode and having anopening which exposes a part of an upper surface of the transparentelectrode, and an organic material layer covering the opening of theinsulating film and a part of the insulating film along the openingthereof to which the current is supplied through the part of the uppersurface of the transparent electrode, a boundary formed between the partof the insulating film and the organic material layer is covered by thelight shielding member in a plan view from the principal surface of thesubstrate.

(1b) At least one of the conductive layers formed as a part of thescanning signal line and one of electrodes of the data storing elementis provided for the light shielding member.

(1c) The light shielding member is provided with a conductive layerformed at the same level as that of the scanning signal line on theprincipal surface of the substrate and is shaped into a ring, a L, or anU in the vicinity of a light emitting region of the organicelectroluminescent element in a plan view from the principal surface ofthe substrate.

(1d) The light shielding member is a part of a wiring layer formed atthe same level as that of at least one of the data signal line and thecurrent supply line on the principal surface of the substrate andsupplying the current to the organic electroluminescent element, and iselectrically connected e.g. to the transparent electrode of the organicelectroluminescent element which receives the current supplied from thesecond active element.

(1e) The light shielding member contains an aluminum layer therein.

(1f) The light shielding member is arranged in each of the plurality ofpixels, and the plurality of active elements and the organicelectroluminescent element are spaced apart from each other along theprinciple surface of the substrate by the light shielding member in eachof the plurality of pixels.

More concrete constitutional examples of the aforementioned secondexample of the organic electroluminescent light emitting display deviceaccording to the present invention will be described as follows,respectively.

(2a) When the organic electroluminescent element includes a transparentelectrode receiving the current supplied from the second active element,an insulating film formed on the transparent electrode and having anopening which exposes a part of an upper surface of the transparentelectrode, and an organic material layer covering the opening of theinsulating film and a part of the insulating film along the openingthereof to which the current is supplied through the part of the uppersurface of the transparent electrode, (2a-1) the first light shieldingmember and the second light shielding member are arranged in each of theplurality of pixels and formed between the principal surface of thesubstrate and the transparent electrode, and (2a-2) at least one of thefirst light shielding member and the second light shielding member isextended from a lower side of insulating to a lower side of the openingof the insulating film.

(2b) At least one of conductive layers formed as a part of the scanningsignal line and one of electrodes of the data storing element is shapedinto the first light shielding member, and the second light shieldingmember is at least one of a conductive layer formed as the one ofelectrodes of the data storing element and a conductive layer connectedto the current supply line.

(2c) One of the first light shielding member and the second lightshielding member is a part of the scanning signal line, and anotherthereof is a conductive layer formed at the same level as that of thescanning signal line on the principal surface of the substrate which isshaped into a ring, a L, or an U in the vicinity of a light emittingregion of the organic electroluminescent element in a plan view from theprincipal surface of the substrate.

(2d) At least one of the first light shielding member and the secondlight shielding member is (2d-1) a part of at least one of the datasignal line and the current supply line, or (2d-2) a part of a wiringlayer formed at a level on the principal surface of the substrate whereat least one of the data signal line and the current supply line isformed and supplying the current to the organic electroluminescentelement (e.g. electrically connected to the transparent electrode of theorganic electroluminescent element which receives the current suppliedfrom the second active element).

(2e) The first light shielding member and the second light shieldingmember contain aluminum layers therein, respectively.

(2f) Each of the plurality of pixels is divided into a region where theplurality of active elements are formed and another region where theorganic electroluminescent element is formed along the principle surfaceof the substrate.

Here, the present invention is not limited to the organic EL lightemitting display device having the above-mentioned structures andvarious modifications can be made without departing from the technicalconcept of the present invention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1(A) and FIG. 1(B) show one example of a pixel provided to anorganic EL light emitting display device according to the presentinvention, wherein FIG. 1(A) shows a planar structure and FIG. 1(B)shows an equivalent circuit thereof;

FIG. 2 is a plan view of a pixel array in which a plurality of pixelsshown in FIG. 1(A) are arranged in a matrix array;

FIG. 3 shows a first photo pattern formed on a photolithography maskused in a step for manufacturing the pixel array shown in FIG. 2;

FIG. 4 shows a second photo pattern formed on a photolithography maskused in the step for manufacturing the pixel array shown in FIG. 2;

FIG. 5 shows a third photo pattern formed on a photolithography maskused in the step for manufacturing the pixel array shown in FIG. 2;

FIG. 6 shows a fourth photo pattern formed on a photolithography maskused in the step for manufacturing the pixel array shown in FIG. 2;

FIG. 7 shows a fifth photo pattern and a sixth photo pattern formed on aphotolithography mask used in the step for manufacturing the pixel arrayshown in FIG. 2 together;

FIG. 8 shows a cross-sectional structure of the pixel of the organic ELlight emitting display device according to the present invention whichis formed on a glass substrate made of soda glass;

FIG. 9 shows a cross-sectional structure of the pixel of the organic ELlight emitting display device according to the present invention whichis formed on a quartz substrate;

FIG. 10(a) to FIG. 10(c) show a cross-sectional structure of one pixel(pixel region PIX) out of a plurality of pixels arranged in the pixelarray shown in FIG. 2, wherein FIG. 10(a) shows a cross-section of aportion taken along a dashed line A-A of the pixel region PIX shown inFIG. 2, FIG. 10(b) shows a cross-section of a portion taken along adashed line B-B of the pixel region PIX shown in FIG. 2 and FIG. 10(c)shows a cross-section of a portion taken along a dashed line C-C of thepixel region PIX shown in FIG. 2;

FIG. 11(a) and FIG. 11(b) are views which schematically show thepositional relationship between a bank end portion and a shield endportion shown in FIG. 10(a) to FIG. 10(c), wherein FIG. 11(a) shows across section of a bank which is formed such that the bank is projectedfrom the shield end portion and FIG. 11(b) shows a cross section of abank which is formed such that the bank end portion remains on an upperportion of the shield;

FIG. 12 shows both variations of a taper angle of bank and contrastratio versus a distance between a tapered edge of the bank and an endportion of the shielding layer;

FIG. 13 shows one example of a cross-sectional structure in the vicinityof a pixel of the organic EL light emitting display device according tothe present invention;

FIG. 14 shows patterns (images) generated on a display screen in anexperiment in which a contrast ratio between the organic EL lightemitting display device according to the present invention and theconventional organic EL light emitting display device are compared;

FIG. 15 is a view showing steps of manufacturing process of the organicEL light emitting display device according to the present inventionwhile mainly focusing on a driver transistor (TFT portion);

FIG. 16 is a view for explaining the arrangement of a group of lines ofthe organic EL light emitting display device according to the presentinvention;

FIG. 17 is a view for explaining the circuit constitution of the organicEL light emitting display device according to the present invention; and

FIG. 18 is a view showing an equivalent circuit of one of pixelsincluded in a pixel array shown in FIG. 17.

DETAILED DESCRIPTION Embodiments of the Invention

FIG. 1(A) is a plan view showing one pixel in one example of an organicEL light emitting display device (also referred to as “organic ELdisplay device”) to which the present invention is applied. FIG. 1(B)shows an equivalent circuit of this pixel (pixel element), whereinswitching elements SW1, SW2, SW3, DT, capacitive elements C1-CSi,CSi-C2, and contact holes (indicated by double square shape in FIG.1(A)) which will be explained later Cont-DL, Cont-PL, and nodes formedas CH1, CH2, CH3 shown in FIG. 1(A) are indicated in FIG. 1(B) in acorresponding manner. Respective capacitive elements are specified byreference characters each of which is indicated by a couple consistingof a semiconductor layer CSi which is formed as a pair of electrodeswhich sandwich an insulation material layer (dielectric layer)therebetween and a conductive layer C1 or C2 which is placed over thesemiconductor layer CSi. Although an organic EL element (light emittingelement) LED which is formed for each pixel is also included in thisequivalent circuit, the full configuration of the organic EL element LEDis not described in FIG. 1(A). In FIG. 1(A), the organic EL element LEDis constituted of a transparent electrode ITO (profile thereof beingindicated by a dashed line) and an organic material layer and anelectrode layer (neither of them being shown in FIG. 1(A)) which aresequentially laminated to the upper surface of the transparent electrodeITO.

In the image display region of the organic EL light emitting displaydevice according to the present invention, a plurality of pixels shownin FIG. 1 are arranged two-dimensionally as shown in FIG. 2 thus forminga so-called active matrix type pixel array. Respective members(semiconductor layer CSi and electrode layers C1, C2) which are includedin the equivalent circuit corresponding to one pixel shown in FIG. 1(B)are substantially surrounded by a frame indicated by a broken line whichcorresponds to the pixel region PIX shown in FIG. 2.

In FIG. 1(A), an octagonal profile indicated by the reference characterOPN shows an opening portion of a bank BMP. The bank BMP is aninsulation layer formed on a periphery of an upper surface of thetransparent electrode ITO. The above-mentioned organic material layer(explained later as member OCT) is brought into contact with the uppersurface of the transparent electrode ITO exposed through the opening.The bank BMP electrically separates among pixels the organic materiallayers formed on the transparent electrodes ITO and the openings OPN aresubstantially aligned with light emitting regions of the organic ELelement LED (see FIG. 1(B)) formed on respective pixels.

On the other hand, in this embodiment, the above-mentioned electrodelayer (referred to as “member CM” later) which constitutes the organicEL element LED by sandwiching the organic material layer together withthe transparent electrode ITO strides over a plurality of pixels and areformed like counter electrodes (common electrodes) in a twistednematic-type (so-called TN-type) liquid crystal display device. To theorganic EL element LED which is indicated as the opening OPN of the bankBPM in FIG. 1(A), an electric current (charge) which passes a currentpath which is formed by sequentially arranging the node CH3, theswitching element DT, the node CH2, the switching element SW2 from abranch line of a current supply line PL is supplied through thetransparent electrode ITO which is electrically connected to the currentpath through the contact hole Cont-ITO. In respective switching elementDT and switching element SW2 (surrounded by circles in FIG. 1(A)), thecurrent path is formed as semiconductor layers (indicated by thickcolor) and electrode layers (indicated by thin color) made of metal oralloy are formed by way of insulation layers. In other words, the flowof charge in the above-mentioned current path is controlled by theswitching element DT and the switching element SW2 formed on the currentpath (electric fields applied to semiconductor layers corresponding tothese switching elements). For example, the charge in the current pathwhich passes the switching element SW2 is controlled by the electricfield applied to the control signal line CL1.

The supply of current to the organic EL element LED in each pixel ofthis embodiment shown in FIG. 1(A) and FIG. 1(B) is controlled inresponse to video signals (voltage signals) supplied from the drain line(video signal line) DL for each pixel. In other words, to the organic ELelement LED, an electric current which corresponds to the video signaltransmitted through the drain line DL is applied. The switching elementSW1 is also referred to as a control transistor. Inside the circle whichindicates such a region, a scanning signal line GL is formed such thatthe scanning signal line GL strides twice over the semiconductor layerelectrically connected to the drain line DL through the node Cont-DL.The gate electrode (here, scanning signal line GL) which crosses twicethe channel layer (semiconductor layer) like the switching element SW1shown in FIG. 1(A) is also referred to as dual gates. The video signaloutputted from the switching element SW1 reaches the conductive layer C1which constitutes one of a pair of electrodes forming the capacitiveelement C1-CSi through a conductive layer which strides over two controlsignal lines CL1 and CL2. Accordingly, to each pixel which belongs toeach row of pixels (a group of pixels arranged in the direction whichcrosses the extending direction of the drain line) arranged parallelalong the drain line, the video signal is inputted from the drain lineDL in response to the scanning signal transmitted through the scanningsignal line GL corresponding to the row of pixels, wherein the voltageis held in the capacitive element C1-CSi until the next video signal isinputted to each pixel. The capacitive element C1-CSi functions like acapacitance constituted of the electric current to the organic ELelement LED. Accordingly, the switching element DT is also referred toas “drive transistor”. As shown in FIG. 1(A) and FIG. 1(B), in thisembodiment, in the circle which indicates the switching element DT, aconductive layer which is electrically connected to anothersemiconductor layer CSi of a pair of electrodes which form thecapacitive element C1-CSi at the node CH1 is formed on an upper portionof the semiconductor layer of the above-mentioned current path.Accordingly, in response to the video signal inputted from the drainline DL, the electric current which responds to the voltage held in thecapacitive element C1-CSi is written in the light emitting region(corresponding to the above-mentioned opening OPN of the bank) of theorganic EL element through the switching element DT.

Here, the scanning signal line GL is formed in a zigzag shape to obviatethe contact holes (indicated by a double square shape in FIG. 1(A))which constitute the above-mentioned node Cont-DL or the like. However,in the image display region as a whole, as exemplified in FIG. 2, thescanning signal line GL extends in the direction which crosses theextending direction of the current supply line PL. In the pixel, thescanning signal line GL extends along the light emitting region (openingOPN) of a pixel (upper side in FIG. 1(A)) which is arranged close to thepixel and is overlapped to the branch line of the above-mentionedcurrent supply line PL. The scanning signal line GL formed in theabove-mentioned manner lies over (next pixel side) respective channellayers (semiconductor layers indicated in thick color) of theabove-mentioned switching elements SW1, SW2, SW3, DT formed in thepixel. Accordingly, by forming the scanning signal line GL using amaterial such as metal, alloy or the like which can easily absorb orreflect light, it is possible to conceal these channel layers from lightwhich is generated at other pixel (upper neighboring pixel in FIG. 1(A))arranged adjacent to and along the drain line DL or the current supplyline PL. Particularly, when the branch line of the current supply linePL is formed of a material which easily absorbs or reflects light, aportion of the scanning signal line GL which is overlapped to the branchline efficiently performs light-shielding of the above-mentionedrespective channel layers (portion of the scanning signal line GL beingsurrounded by a circle which indicates a light shielding layer GLS inFIG. 2). Such a scanning signal line GL constitutes one of features ofthe light shielding structure according to the present invention. Theabove-mentioned light shielding structure may be formed by the controlsignal lines CL1, CL2 extending in the direction which crosses theextending direction of the drain line DL and the current supply line PLin place of the scanning signal line GL.

As shown in FIG. 1(A) and FIG. 1(B), in each pixel expressed by thisembodiment, two control signal lines CL1, CL2 and the switching elementsSW2, Sw3 which are controlled by either of the control signal lines CL1,CL2 are provided. In a so-called current-driven type organic EL lightemitting display device which controls the luminance in response to acurrent supply quantity to the organic EL element LED, the arrangementof these control signal lines CL1, CL2 and switching elements SW2, SW3is not always necessary in view of the operational principle. Forexample, with respect to an organic EL light emitting display deviceshown in FIG. 17 and a pixel structure thereof shown in FIG. 18, theyare not provided with these control signal lines and switching elements.So long as there is no irregularities with respect to thecharacteristics (particularly “threshold voltage value”) of the drivetransistors arranged in respective pixels or such irregularities can beignored, it is possible to practically use the organic EL light emittingdisplay device having the pixel structure shown in FIG. 18. Moreover,the organic EL light emitting display device having the pixel structureof FIG. 18 can be also used practically by modulating brightness of eachpixel thereof while a voltage applied to the channel of the drivetransistor DT in FIG. 18 is swung in a range in which the drivetransistor DT responds linearly to the voltage. However, when thechannel layers of the drive transistors DT are formed of polycrystal orpseudo-single crystal of semiconductor material such as silicon, it isdifficult to deny that the conditions for crystallizing process (forexample, annealing by laser irradiation) differ between pixels. Thedifference in the conditions for crystallizing process allows thecoexistence of the pixels which differ in the characteristics of thedrive transistors DT within the image display region of one organic ELlight emitting display device. As a result, it gives rise to theirregularities of luminance (luminance irregularities) within the imagedisplay region of the organic EL light emitting display device to whichthe image data for displaying the whole screen with the same gray scaleis inputted.

According to this embodiment, one of reasons why two control signallines CL1, CL2 and the switching elements SW2, SW3 which are controlledby either of the control signals CL1, CL2 are provided is to make thecharacteristics of the drive transistors DT which become non-uniformwithin the image display region substantially uniform. These functionsare explained as follows. To the control signal lines CL1 and CL2,control signals which differ in respective timing are supplied from acontrol signal supply circuit not shown in FIG. 1(A) and FIG. 1(B).

To be more specific, first of all, the control signals transmittedthrough the control signal line CL1 turn on the switching element (firstinput switch) SW2. Here, although the drive transistor DT is not turnedon, the node CH2 side of the drive transistor DT is connected to thereference potential through the organic EL element LED from the floatingstate and the potential is raised to a given value. Subsequently, thecontrol signal transmitted through the control signal line CL2 turns onthe switching element (second input switch) SW3 which corresponds to thecontrol signal. Due to such a constitution, one electrode CSi of thecapacitive element CSi-CS2 which was in the floating state is connectedto the node CH2 side of the drive transistor DT through the switchingelement SW3 and the potential is raised to the above-mentioned givenvalue. Here, since the gate potential (potential of the node CH1) of thedrive transistor DT is equal to the output-side potential (potential onthe node CH2 side), the channel layer of the drive transistor DTinterrupts the flow of charge. Since a given electric current flows inthe current supply line PL irrespective of the video signal transmittedthrough the drain line DL, the potential of the current supply line isalso substantially fixed. Accordingly, by sequentially turning on twoswitching elements SW2, SW3 (by sequentially bringing respective channellayers into a conductive state), a substantially same quantity of chargeis stored in the capacitive element CSi-C2 of any pixel. When thechannel layer of the switching element SW3 is closed in this state andthe switching element (control transistor) SW1 is turned onsubsequently, in response to the voltage (video signal) applied to oneelectrode C1 of the capacitive element C1-CSi, the capacity of thecapacitive element C1-CSi is also changed. In response to this change ofcapacity, there arises a difference between the potential of the nodeCH1 (gate potential of the drive transistor DT) and the potential on theoutput side (node CH2 side). Due to this potential difference, in thepixel described in this embodiment, by turning on the drive transistorDT and by controlling a quantity of charge which flows in the turned-onchannel, the organic EL element LED is lit with given luminance.

Although the channel layer of the drive transistor DT is usually turnedon with respect to a given gate potential (threshold voltage) Vth, whenthe channel layer is formed of a polycrystalline layer or a pseudosingle crystal layer of semiconductor material, for example, asmentioned above, the threshold voltage Vth differs corresponding torespective pixels. In this embodiment, an operating point of the drivetransistor DT which is dependent on such a threshold voltage Vth is setusing the potential of the node CH1 given by the capacitive elementCSi-C2 as the reference, and the ON-OFF of the drive transistor DT iscontrolled based on the balance of capacity between the capacitiveelement CSi-C2 and the capacitive element C1-CSi so as to stabilize thethreshold voltage Vth whereby the irregularities of the threshold valueVth which are generated among the pixels is corrected. The detail of therespective operations of the switching elements SW1, SW2, SW3 and DT isexplained hereinafter.

The switching element SW1 which is also referred to as the controltransistor is a switch which inputs the video signal voltage to everypixel. This switching element SW1 is provided not only to thisembodiment but also to a pixel of an organic EL light emitting displaydevice which controls the conductive state of a channel layer of a drivetransistor DT using the threshold voltage Vth. The switching element SW1is turned on or off in response to the scanning signal transmittedthrough the scanning signal line GL which crosses the channel layer(semiconductor layer) of the switching element SW1, and writes in thevideo signal voltage inputted from the drain line DL to a capacitiveelement (capacitor) of a so-called pixel circuit provided to everypixel.

In writing in the image data to the image display region of the organicEL light emitting display device which drives the organic EL elementprovided to each pixel by current injection one time for every frame(vertical scanning period), for example, a period in which the switchingelement SW1 formed in each pixel is turned on is limited to a horizontalscanning period allocated to every scanning signal line GL. Accordingly,a current injection quantity (charge injection quantity) to the organicEL elements included in the pixel line which corresponds to eachscanning signal line GL is also restricted.

In such a current driving type organic EL light emitting display device,different from a voltage driving type display device such as a TN typeliquid crystal display device, it is difficult to maintain the luminanceof the pixel for a given period at the switching element SW1 whichacquires the image data (video signal). Accordingly, as mentioned above,another switching element which is also referred to as the drivetransistor DT and a current supply line PL are provided to every pixelso as to maintain the conductive state of the channel layer for a givenperiod whereby the luminance of each pixel is ensured. The capacitiveelement which is connected to the output side of the switching element(control transistor) SW1 holds the gate potential of the above mentioneddrive transistor DT at a desired value for a given period and continuesthe current injection to the organic EL element LED. Accordingly, inboth of the case in which the conductive state of the drive transistorDT is controlled using the threshold voltage Vth as the reference andthe case in which the drive transistor DT is controlled in accordancewith this embodiment, it is recommendable to provide the capacitiveelement to the output side of the switching element SW1.

In the switching element SW1 of this embodiment, as shown in FIG. 1(A),the channel layer has a dual gate structure which crosses the abovementioned scanning signal line GL at two portions thereof. Due to thecontrol performed at these two portions, the operation to write in thesignal voltage supplied from the drain line DL to one electrode C1 ofthe capacitive element C1-CSi is stabilized. Further, due to this dualgate structure, leaking of charge stored in the electrode (conductivelayer C1 in this embodiment) on the switching element SW1 side (drainline DL side) of the capacitive element can be suppressed whereby thegate potential of the drive transistor DT is stabilized for a givenperiod.

The switching element SW2 not only controls the storage of charge to oneelectrode (semiconductor layer) CSi of the above mentioned capacitiveelement CSi-C2 but also functions as a current supply switch for theflow of current from the drive transistor DT to the organic EL elementELD. The latter function is to write the current which is supplied fromthe current supply line PL and is adjusted in response to the videosignal inputted from the drain line at the drive transistor DT to theorganic EL element LED when the switching element SW2 is turned on. Thislatter function is used not only in this embodiment but also in the casein which the conductive state of the drive transistor DT is controlledusing the threshold voltage Vth as the reference. Such a switchingelement (current supply switch SW2) is subjected to the ON-OFF controlat the timing of the control signal line CL1.

The switching element SW3 is a switch controlling to make the capacitor(condenser) memorize the threshold voltage Vth of the drive transistorDT and constitutes a switching element peculiar to the pixel circuit ofthis embodiment shown in FIG. 1(B).

As shown in FIG. 1(A), in the drive transistor DT, the conductive layerwhich covers the channel layer (semiconductor layer) has a relativelylarge gate length which is elongated along the extending direction ofthe channel layer compared to other switching elements SW1, SW2 and SW3.The drive transistor DT of this embodiment is turned on based on thebalance between the charge stored in the capacitive element CSi-C2through the above mentioned switching element (timing switch) SW3 andthe charge stored in the capacitive element C1-CSi through the abovementioned switching element (control transistor) SW1. Due to such aconstitution, an electric current corresponding to the video signalsupplied from the drain line DL passes the contact hole CH3 formed inthe branch line of the electric supply line PL, and flows to a positionarranged in front of the above mentioned switching element (currentsupply switch) SW2. Further, when the current supply switch SW2 isturned on, the electric current of the current supply line PL is writtenin the organic EL element LED.

FIG. 2 is a plan view in which the above mentioned pixels in FIG. 1(A)are arranged in a matrix array. One pixel shown in FIG. 1(A) correspondsto the pixel region PIX surrounded by a bold broken line in FIG. 2. Theorganic EL light emitting display device according to the presentinvention is provided with the image display region having the activematrix structure in which the pixels shown in FIG. 1(A) are arrangedtwo-dimensionally as shown in FIG. 2.

One electrodes (semiconductor layers) CSi which are respectivelyprovided to the capacitive elements (capacitors) C1, CSi, CSi-C2included in the equivalent circuit of one pixel shown in FIG. 1(B) aredescribed as regions of thick color which extend from the upper side tothe right side of the bank opening OPN (light emitting region providedwith organic material layer OCT) of the pixel region PIX shown in FIG.2. Another electrode C1 of the capacitive element C1-CSi also extendsfrom the upper side to the right side of the bank opening OPN and isformed over the above mentioned semiconductor layer CSi by way of aninsulation material layer (dielectric layer). Another electrode C2 ofthe capacitive element CSi-C2 is formed above the semiconductor layerCSi which extends toward the right lower side of the bank opening OPN byway of an insulation material layer (dielectric layer) and iselectrically connected to the current supply line PL formed above and atthe contact hole Cont-PL formed at the right lower corner of the pixelregion.

To the semiconductor layers CSi which constitute the above-mentioned oneelectrodes respectively at the capacitive elements C1-CSi, CSi-C2, thecharge is supplied through the switching elements SW2, SW3. To anotherelectrode C1 (indicated by color thinner than color of semiconductorlayer CSi) of the capacitive element C1-CSi, the charges are suppliedfrom the drain line DL formed on the left end of the pixel region PIXthrough the contact hole Cont-DL and the switching element SW1. Toanother electrode C2 (indicated by color thinner than color ofsemiconductor layer CSi) of the capacitive element CSi-C2, the charge issupplied from the current supply line PL formed on the right end of thepixel region PIX through the contact hole Cont-PL.

To describe in a strict sense, respective portions of the semiconductorlayer CSi and the conductive layers C1, C2 which correspond to the pixelregions PIX shown in FIG. 2 are projected outwardly from the right endof the frame of a broken bold line indicating the pixel region PIX,while respective portions of the semiconductor layer CSi and theconductive layers C1, C2 which correspond to pixel regions arranged onthe left side of the pixel region PIX enter the inside of pixel regionPIX from the left end of a frame of a bold broken line which indicatesthe pixel region PIX.

As described above, in the organic EL light emitting display deviceshown in this embodiment, the charges which are stored respectively inthe semiconductor layer CSi and the conductive layers C1, C2 whichconstitute two capacitive elements (capacitors) formed corresponding tothe pixel region PIX determine a current quantity which is written inthe light emitting regions (organic material layer OCT formed in thebank opening OPN) of the organic EL element from the branch line of thecurrent supply line PL which extends to the upper end of the pixelregion PIX through the contact hole CH3, the switching element DT whichconstitutes the drive transistor and the contact hole Cont-ITO. Here, inthe pixel region PIX in FIG. 2, the transparent electrode layer ITOshown in FIG. 1(A) is omitted.

In the organic EL light emitting display device according to thisembodiment, as the switching elements SW1, SW2, SW3 and the drivetransistor DT which are provided for every pixel, a field effect typetransistor (also referred to as “thin film transistor” or Poly-SiTFT)having a channel layer formed of poly-crystalline silicon (also referredto as Poly-Si) is used. In the display device which drives a pluralityof pixels arranged in the image display region respectively using theswitching elements of this type (Poly-SiTFT), due to a photovoltaiceffect which appears when light is irradiated to the channel layer(poly-crystalline layer) of the switching element provided to eachpixel, the conductive state of the channel layer is liable to be easilyfluctuated and hence, there may be a case that the luminance of thepixel driven by the switching element (TFT) is deviated from a givenvalue and brings about the degradation of the image quality of the imagedisplay region. Particularly, in the pixel of the active matrix typeorganic El light emitting display device, since the organic EL element(light emitting portion) and the active element (switching element)which controls the organic EL element are arranged close to each other,light having intensity of several hundred thousands lux is irradiatedtoward the channel layer of the switching element from the obliquedirection. For example, even when a light shielding structure similar tothat of the conventional TFT liquid crystal display device described inU.S. Pat. No. 5,561,440 is applied to the pixel of the organic EL lightemitting display device, it is impossible to shield the channel layer ofthe switching element from this strong light. Accordingly, in thepresent invention, as illustrated in this embodiment, the electrodelayer of the capacitive element (capacitor) of the circuit (pixelcircuit) formed on every pixel is arranged between the channel layer ofthe switching element made of polycrystalline silicon (Poly-Si) and thelight emitting portion of the organic EL element as a light shieldingmaterial so as to prevent the degradation of the image displayed by theorganic EL light emitting display device.

In one pixel region PIX surrounded and indicated by a bold broken linein FIG. 2, the conductive layer C1 which constitutes one electrode ofthe capacitive element C1-CSi mounted on every pixel of the organic ELlight emitting display device is formed of material having low opticaltransmissivity (for example, high-melting-point metal such asmolybdenum-tungsten (MoW), titanium-tungsten (TiW), an alloy thereof, oran silicide thereof) between the bank opening portion OPN where thelight emitting portion (organic material layer OCT) is provided and agroup of switching elements (SW1, SW2, SW3, DT). On the other hand, inthis embodiment, another electrode of the above-mentioned capacitiveelement C1-CSi is formed of polycrystalline silicon layer CSi togetherwith the channel layers of the above-mentioned switching elements SW1,SW2, SW3 and DT. Since the polycrystalline silicon layer CSi absorbslight incident on the layer CSi by 90% at maximum, together with theabove-mentioned one electrode (conductive layer C1) of the capacitiveelement formed above the the polycrystalline silicon layer CSi, it ispossible to prevent light from the above-mentioned light emittingportion (organic material layer OCT) from being irradiated to respectivechannel layers of the above-mentioned group of the switching elements inthe pixel region PIX.

As shown in FIG. 1(A) and FIG. 2, in each pixel of the organic EL lightemitting display device according to the present invention, theconductive layers CSi, C1 and C2 which constitute electrodes of twocapacitive elements (capacitors) C1-CSi, CSi-C2 which are formedrespectively in the pixel are also formed below the current supply linePL and the drain line DL. In this manner, by extending the conductivelayers CSi, C1, C2 along the current supply line PL which is arrangedbetween the pixel regions and the drain line DL which is arranged closeto and parallel to the current supply line PL, the capacitor regions(area in which a pair of electrodes face each other in an opposedmanner) of the capacitive elements C1-CSi, CSi-C2 are enlarged atmaximum and the light emitting region in the pixel region PIX can beexpanded at maximum. As described above, the organic EL light emittingdisplay device makes the light emitting portion of each pixel subjectedto the current driving and hence, even when the electrodes C1, C2 of theabove-mentioned capacitive elements C1-CSi, CSi-C2 are made to face thecurrent supply line PL and the drain line DL, a crosstalk is hardlygenerated.

The above-mentioned capacitive elements C1-CSi, CSi-C2 are not limitedto the structure in which the capacitive elements C1-CSi, CSi-C2 areoverlapped to both of the current supply line PL and the drain line DLwhich are arranged parallel between the neighboring pixels. That is,depending on the largeness of the capacity regions corresponding to thecapacities which are respectively requested to the capacitive elementsC1-CSi, CSi-C2, the capacitive elements may be overlapped to either oneof the current supply line PL and the drain line DL. In both cases, thecapacitive element C1-CSi (portion) and the capacitive element CSi-C2interrupts leaking of light generated between the neighboring pixels inthe extending direction of the scanning signal lines GL. In the organicEL light emitting display device, the capacitive element C1-CSi which isprovided for every pixel is necessary to hold the signal voltage (videosignal) from the drain line DL. However, it is not necessary to extendthe capacitive element C1-CSi below at least one of the current supplyline PL and the drain line DL so as to make the capacitive elementC1-CSi perform a function of a shielding member to obstruct lightbetween the above-mentioned pixels. That is, leaking of light betweenthe neighboring pixels along the scanning signal lines GL can besuppressed by at least one of the capacitive element C1-CSi and thecapacitive element CSi-C2. Here, it is unnecessary that one electrode C2of the capacitive element CSi-C2 is connected to the current supply linePL through the contact hole Cont-PL as shown in FIG. 1(A) and FIG. 2 andthe potential of one electrode C2 may be held at the floating state, forexample.

In the embodiment shown in FIG. 2, a boundary between theabove-mentioned two conductive layers C1 and C2 appears in the vicinityof the longitudinal center of the pixel region PIX. From a viewpoint ofshielding function to cope with the above-mentioned leaking of lightbetween the pixels, it is desirable that a discontinuing portion of theshield member (light shielding member) is not formed in the vicinity ofthe center of the light emitting portion (organic material layer OCT).For example, it is preferable that the whole shielding member betweenthe pixels is formed of the capacitive element C1-CSi. Further, in placeof the above-mentioned capacitive element C1-CSi and the capacitiveelement CSi-C2, a shielding member having a ring shape, an L shape or aU shape which is electrically independent from the pixel circuit may benewly provided. Further, the ring-shaped shielding member whichsurrounds the pixel region PIX may be formed in a discontinuing mannerat a position sufficiently remote from the center of the light emittingportion (organic material layer OCT) (for example, corner portion ofpixel region PIX) and hence, a portion of the shielding member may bereplaced with a portion GLS of the scanning signal line GL shown in FIG.2. Further, it may be possible to newly provide a ring-shaped conductivelayer which is electrically separated from the scanning signal line asthe shielding member on the same level as the scanning signal line GL.

As shown in FIG. 2, in the pixel region PIX, the capacitive elementC1-CSi is provided between the scanning signal line, the control signallines CL1, CL2 and the opening portion OPN (light emitting portionformed of organic material layer OCT) of the bank and a portion GLS ofthe scanning signal line GL is arranged at an end portion of the pixelregion PIX. Due to such a constitution, light from the opening portionOCT of the bank is hardly irradiated to respective channel layers of agroup of switching elements (SW1, SW2, SW3, DT) formed inside the pixelregion PIX. Further, by arranging the capacitive elements C1-CSi and theCSi-C2 in such a manner that they overlap the current supply line PL andthe drain line DL extending along the end portion of the pixel regionPIX, lights from two neighboring pixels are hardly mixed to each other.Accordingly, in the organic EL light emitting display device of thisembodiment, desired light emitting quantities (luminance) are obtainedfrom respective organic EL elements which are arranged in the imagedisplay region so that beautiful and clear images can be displayed.

As mentioned above, in the organic EL light emitting display device, itis possible to generate strong light at the organic EL element arrangedat each pixel region PIX. When such strong light is irradiated to theswitching element provided with the channel made of polycrystallinesilicon (Poly-Si) (SW1, SW2, SW3, DT in this embodiment), the siliconlayer (Si layer) which constitutes the channel gives rise to aphotovoltaic effect in accordance with an electric field appliedthereto. Accordingly, an electric field generated in the channel (Silayer) generates a hole-electron pair inside thereof in spite of thefact that the switching element applies an electric field of theturn-off state to the channel and hence, the charge holdingcharacteristics of the switching element is deteriorated. For example,the charge (determining control voltage of drive transistor DT) storedin the capacitive element C1-CSi is leaked to the drain line DL throughthe channel of the switching element (control transistor) SW1 in theturn-off state and, as a result, the electric current supplied to theorganic EL element through the drive transistor DT is decreased. Such aproblem is not apparent in the conventional TFT type liquid crystaldisplay device and hence, it is impossible for the light shieldingstructure which has been adopted by such a liquid crystal display deviceto shield the switching element from the strong light irradiated fromthe organic EL element. Particularly, in the organic EL light emittingdisplay device of the bottom emission scheme which sequentiallylaminates the transparent electrode ITO, the organic material layer OCTand the electrode layer from the substrate main surface side (TFTsubstrate side) and emits light generated at the organic material layerOCT to the TFT substrate side as in the case of this embodiment, lightirradiated from the pixel region PIX is liable to be irradiated to thechannel of the switching element formed on the pixel region PIX andhence, the image quality of the display image is liable to be degradeddue to the control of the switching element (so-called TFT driving).

Accordingly, in the organic EL light emitting display device accordingto this embodiment, it is designed such that the respective electrodes(conductive layers) C1, C2 of the above-mentioned capacitive elementsC1-CSi, CSi-C2 also function as light shielding layers. To be morespecific, as shown in FIG. 2, the capacitive elements C1-CSi, CSi-C2 arearranged at both ends of the opening portion OPN of the bank along thecurrent supply line PL and the drain line DL and these capacitiveelements C1-CSi, CSi-C2 expand respective widths thereof along theextending direction of the scanning signal line GL (direction whichcrosses the extending direction of the current supply line PL or thedrain line DL). Due to such a constitution, it is possible to obstructlight which leaks in the extending direction of the scanning signal lineGL in FIG. 2 with the electrodes C1, C2. When the areas of theelectrodes C1, C2 are restricted to ensure desired capacities requiredby the capacitive elements C1-CSi, CSi-C2, a line M1 which supplies anelectric current from the current supply line PL to the transparentelectrode finally (see FIG. 1(A), the detail of the line M1 beingexplained later and the line also being referred to as referencecharacter ALS) is elongated or the width of at least one of the currentsupply line PL and the drain line DL is widened so as to form lightshielding layers which replace the electrodes C1, C2.

Further, as shown in FIG. 2, a portion of the electrode (conductivelayer) C1 of the capacitive element C1-CSi is formed between the lightemitting region (bank opening OPN) and the switching elements SW1, SW2,SW3 so as to achieve light shielding of the inside (upper side of thelight emitting region) of the pixel region PIX. A portion of theelectrode C1 which is arranged adjacent to the upper end of the openingOPN of the bank has, to enhance the light shielding effect thereof, awidth thereof expanded along the current supply line PL or the drainline DL. Further, the electrode C1 is provided with the contact holeCont-ITO which connects the line M1 and the above-mentioned transparentelectrode ITO electrically at an upper portion thereof as shown in FIG.1(A).

Further, in this embodiment, to perform light shielding of the lowerside of the pixel electrode PIX (the end portion which is arranged closeto another pixel region along the current supply line PL or the drainline DL of the pixel region PIX), a portion GLS of the scanning signalline which contributes to driving of the another pixel electrode isarranged as a light shielding layer at an upper end of another pixelregion. To observe this constitution from the inside of the pixel regionPIX, a portion GLS of the above-mentioned scanning signal line performsthe light shielding of the switching element SW1 arranged at the lowerside of such a portion from the light emitting region of another pixelregion which is arranged close to the upper side of the pixel regionPIX.

As has been explained above, in the organic EL light emitting displaydevice according to the present invention illustrated in thisembodiment, the capacitive elements (capacitors) and the scanning signalline which are provided to every pixel region are arranged at the upperside, the lower side, the left side and the right side of the lightemitting region (organic material layer OCT) respectively so as toprevent light from the organic material layer OCT from being irradiatedto the switching elements SW1, SW2 and SW3. The above-mentionedphotovoltaic effect which appears in the channel layers of the switchingelements does not give any serious influence to the function (turning onwithin a light emitting period of the light emitting region) compared tothe influence given to respective functions of the switching elementsSW1, SW2 and SW3. Accordingly, with respect to four switching elementsarranged in the pixel region PIX, although the drive transistor DT canbe arranged close to the light emitting region compared to other threeswitching elements, as shown in FIG. 2, it is desirable to arrange thedrive transistor DT in a spaced-apart manner from the light emittingregion (a light emitting region OPN′ at the upper side of the pixelregion PIX) and the light shielding member (a portion GLS of thescanning signal line). Further, the current supply line PL which isformed on the electrodes (conductive layers) C1, C2 of the capacitiveelements C1-CSi, CSi-C2 in an overlapped manner can also perform lightshielding against leaking of light in the same manner as theseelectrodes C1, C2.

The pixel array (a portion of the image display region) provided to theorganic EL light emitting display device of this embodiment shown inFIG. 2 is formed by photolithography using mask of 6 type photo patternsshown in FIG. 3 to FIG. 7. With respect to the photo patternsrespectively shown in FIG. 3 to FIG. 7, to facilitate the correspondenceto the pixel array structure shown in FIG. 2, a region which correspondsto the pixel region PIX illustrated in FIG. 2 is surrounded by a boldbroken frame PIX.

In FIG. 3, FIG. 4 and FIG. 6, to focus on the pixel region PIXexclusively, only a group of rectangular patterns of contact holes (forexample, Cont-DL, CH3) shown in FIG. 5 which are relevant to electricalconnections with the semiconductor layers and conductive layers formedby respective photo patterns are depicted. Further, in FIG. 3, FIG. 4and FIG. 6, the bank openings OPN, OPN′ of the pixel region PIX andanother pixel region which is closely arranged at the upper side of thepixel region PIX are indicated by thin broken line frames. Further, inFIG. 6 and FIG. 7, to focus on the pixel region PIX exclusively, thereis shown the rectangular contact hole Cont-ITO which electricallyconnects the line M1 shown in FIG. 1(A) and the transparent electrodeITO which constitutes a portion of the organic EL element. Theseconstitutional features are, as can be understood from the photopatterns other than the pixel region PIX, not included in the photopatterns corresponding to respective drawings. Reference characterswhich discriminate these in FIG. 3, FIG. 4 and FIG. 6 are indicated byan italic font.

FIG. 3 shows a first photo pattern used for the formation of the pixelarray in which a plurality of pixels in FIG. 2 are arranged in a matrixarray. When the quartz substrate is used as the above-mentioned TFTsubstrate, thin films and openings which constitute the pixel array aresequentially formed on a main surface of the quartz substrate by aphotolithography using seven masks on which the first photo pattern tothe seventh photo pattern explained hereinafter are depicted. When thesoda glass is used as the TFT substrate, thin films and openings whichconstitute the pixel array are sequentially formed on the insulationfilm IA which is formed on a main surface of the soda glass in the samemanner. Here, in the photolithography performed sequentially using thephoto patterns consisting the first to sixth photo patterns, the pixelcircuit which drives the organic EL element at each pixel region iscompleted. In this embodiment, the channel of the switching elementincluded in the pixel circuit is formed of an amorphous silicon layerand the amorphous silicon layer is converted into a polycrystallinesilicon layer using a relatively-low-temperature process such as laserirradiation so as to enhance the electron mobility in the channel.Accordingly, a series of processes ranging from the first photo patternto the sixth photo pattern are also referred to as low temperaturePoly-Silicon processes or LTPS processes. On the other hand, in thephotolithography which uses the seventh photo pattern, the bank openingOPN which constitutes the light emitting portion of the organic ELelement is formed. Accordingly, the process using the seventh photopattern is also referred to as organic light-emitting diode process orOLED process. By performing these LTPS process and OLED process, theorganic EL light emitting display device having the pixel array shown inFIG. 2 is completed.

In the first photo pattern shown in FIG. 3, a pattern in which thechannel region of the switching element (TFT in this embodiment) andsilicon layers (Si layers) which constitute substrate-side (lower)electrodes of the capacitive elements (capacitors) C1-CSi, CSi-C2 whichare included in the pixel circuit are colored is formed. To be morespecific, the channel regions FG (SW1), FG (SW2), FG (SW3) and FG (DT)of the switching elements SW1, SW2, SW3, DT formed of polycrystallinesilicon layers and the silicon regions CSi which face theabove-mentioned conductive layers C1, C2 are formed. Here, the siliconregion CSi alleviates a stepped portion of the first insulation film (agate insulation film GI of the switching element shown in FIG. 8 andFIG. 9) formed on an upper surface of the silicon region CSi thuspreventing the rupture of the above-mentioned conductive layer formed onthe insulation film. Among the semiconductor layers which are formed inthe photolithography processes using the mask on which the first photopattern is formed, the semiconductor layers which are used in respectivechannels of the switching elements are hereinafter also generallyreferred by the reference character FG in the following explanation.

FIG. 4 shows the second photo pattern used for the formation of thepixel array shown in FIG. 2. Using this second photo pattern, on theabove-mentioned first insulation film, the scanning signal line GL (alsofunctioning as the control electrode SG (SW1) of the switching elementSW1), the control signal lines CL1, CL2, the conductive layers C1, C2which constitute the upper electrodes of the capacitive elements C1-CSi,CSi-C2 and the control electrode SG (DT) of the drive transistor arecollectively formed as a colored pattern shown in FIG. 4. The controlsignal line CL1 controls the supply of current to the organic EL elementLED shown in FIG. 1(B) and applies a control signal to the controlelectrode SG (SW2) of the switching element SW2 which adjusts thedriving conditions of the drive transistor DT. Further, in thisembodiment in which the capacitive element CSi-C2 is provided to thepixel circuit for adjusting the driving conditions of the drivetransistor DT, there is provided the switching element SW3 whichsupplies a given charge to the capacitive element CSi-C2 so as to adjustthe current supplied to the organic EL element LED in response to thevideo signal. Accordingly, in this embodiment, there is also providedthe control signal line CL2 which applies a control signal to thecontrol electrode SG (SW2) of the switching element SW3. Among theconductive layers which are formed in the photolithography processesusing the mask on which the second photo pattern is formed, theconductive layers which are used as respective control electrodes of theswitching elements (including the drive transistor DT) are hereinafteralso generally referred by the reference character SG in the followingexplanation.

As mentioned above, the scanning signal line GL has a function ofcontrolling the acquisition of the video signal in the channel region ofthe switching element SW1 to the pixel region as well as a function ofobstructing light leaked toward a group of switching elements of thepixel region from another pixel region arranged close to the pixelregion. Accordingly, as shown in FIG. 4, the scanning signal line GL isformed in a step shape which repeats bending with respect to theextending direction of the scanning signal line GL (lateral direction inFIG. 4). From a viewpoint of enhancing the light shieldingcharacteristics of the scanning signal line GL, it is preferable to makethe portion GLS which also has a light shielding function approach anend of the pixel region (that is, a light emitting portion OCT ofanother pixel region arranged close to the pixel region) as close aspossible. Further, the upper electrodes (conductive layers) C1, C2 ofthe capacitive elements C1-CSi, CSi-C2 which are formed together withthe scanning signal line GL are also required to have the lightshielding function as mentioned previously. Accordingly, the conductivelayers which are formed using the second photo pattern are formed with amaterial and a thickness suitable for suppressing the opticaltransmissivity thereof. As the material of the conductive layers, byfocusing on the absorbance and the reflectance, a high-melting-pointmetal (refractory metal) as exemplified by molybdenum (Mo), tungsten(W), titanium (Ti), chromium (Cr), an alloy thereof and a silicidethereof are recommended from a viewpoint of the absorbance, whilealuminum (Al) and an alloy thereof are recommended from a viewpoint ofthe reflectance. These materials may be laminated in a plural layers.

Although the portion GLS of the scanning signal line which alsofunctions as the light shielding member is configured to have a widthequal to the width of the portion which constitutes the controlelectrode SG (SW1) of the switching element SW1, the width of theportion GLS of the scanning signal line may be increased compared to thewidth of other portions of scanning signal line GL so as to enhance thelight shielding performance. Due to such a constitution, the lightshielding characteristics with respect to the pixel region (indicated atthe upper side of the pixel region PIX, for example, in FIG. 4) which isconnected to the scanning signal line of next stage is enhanced.Further, in this embodiment, although the scanning signal line GL isformed in a step shape, it may be formed in a straight line in the samemanner as the conventional TFT type liquid crystal display elementdriven by the active matrix type method. The shape of the scanningsignal line GL may be suitably changed corresponding to the number andthe arrangement of the switching elements formed every pixel region.

FIG. 5 shows the third photo pattern used in the formation of the pixelarray shown in FIG. 2. The third photo pattern is a pattern for formingthe contact holes which are dug toward the main surface of the substrate(TFT substrate) from an upper surface of the second insulation film (aninsulation film IB shown in FIG. 8 and FIG. 9, for example) which coversthe conductive layer of the scanning signal line GL or the like which isformed using the second photo pattern. Respective contact holes formedusing this pattern are served for electrically connecting the conductivelayer (formed on the above-mentioned second insulation film) which willbe explained later in conjunction with the fourth photo pattern shown inFIG. 6 and either one of the semiconductor layer formed using the firstphoto pattern and the conductive layer formed using the second photopattern. Accordingly, out of 12 contact holes indicated inside the pixelregion PIX shown in FIG. 5, 9 contact holes (including the contact holesCont-DL, CH1, CH2 and CH3) are also shown on upper surfaces of thesemiconductor layers (CSi, FG) in the pixel region PIX shown in FIG. 3.Further, out of 12 contact holes shown in the pixel region PIX shown inFIG. 5, 3 remaining contact holes (including the contact hole Cont-PL)are also shown on upper surfaces of the conductive layers (C1, C2, SG(DT)) in the pixel region PIX shown in FIG. 4.

The function of the contact holes shown in FIG. 5 are briefly explainedby taking the contact holes Cont-PL and Cont-DL as an example inconjunction with FIG. 1(B) and FIG. 2. The contact hole Cont-PL isserved for connecting the upper electrode (conductive layer) C2 of thecapacitive element CSi-C2 formed on the above-mentioned first insulationfilm using the second photo pattern and the current supply line PL whichis formed on the above-mentioned second insulation film using the fourthphoto pattern shown in FIG. 6 through the second insulation film. Inresponse to a storage quantity of charge in the lower electrode(semiconductor layer) CSi of the capacitive element CSi-C2 which ischanged at the timing of applying the control signal (scanning signal)to the switching element SW1 from the scanning signal line GL, thecharge is supplied to the upper electrode (conductive layer) C2 from thecurrent supply line PL via the contact hole Cont-PL.

On the other hand, the contact hole Cont-DL is served for connecting oneend (also referred to as the drain region) of the channel layer FG (SW1)of the switching element (control transistor) SW1 which is formed usingthe first photo pattern and is covered with the above-mentioned firstinsulation film and the drain line DL formed on the above-mentionedsecond insulation film using the fourth photo pattern through the firstand second insulation films. When the channel layer FG (SW1) of theswitching element (control transistor) SW1 is turned on due to theapplication of the control signal from the scanning signal line GL, thevideo signal (voltage signal) from the drain line DL is applied to theupper electrode C1 of the capacitive element C1-CSi through the contacthole Cont-DL and the channel layer FG (SW1). A charge quantity which isstored in the capacitive element C1-CSi controls the voltage applied tothe control electrode SG (DT) of the drive transistor DT together with acharge quantity stored in the capacitive element CSi-C2. Accordingly, inresponse to the timing that the switching element SW1 is turned on, anelectric current corresponding to the video signal is supplied to thechannel FG (DT) of the drive transistor DT. The electric currentcorresponding to the video signal is written in the transparentelectrode ITO through the switching element SW2, the line M1 and thecontact hole Cont-ITO. An electric current corresponding to the videosignal which is written in the transparent electrode ITO flows intoanother electrode CM (explained later in conjunction with FIG. 8 andFIG. 9) which is included in the organic EL element LED together withthe organic material layer OCT through the organic material layer OCTformed on the transparent electrode ITO so that the organic materiallayer OCT (an electro-luminescence material layer included in theorganic material layer) is made to generate light.

FIG. 6 shows the fourth photo pattern used in the formation of the pixelarray shown in FIG. 2. Using the fourth photo pattern, the currentsupply line PL and the branch line PLB thereof, the drain line DL andrespective lines M1, M2, M3 and M4 which are connected to at least oneof a group of switching elements (SW1, SW2, SW3, DT) including theabove-mentioned drive transistor are formed on the above-mentionedsecond insulation film as a colored pattern shown in FIG. 6.

The line M1 is formed as a current path provided between the output sideof the switching element SW2 and the node (contact hole) Cont-ITOconnected to the transparent electrode ITO of the organic EL elementLED. The line M2 is formed as a charge path which is provided betweenone end of the drive transistor DT and one end of the switching elementSW3. The line M3 electrically connects another end of the switchingelement SW3, the semiconductor layers CSi which constitute lowerelectrodes of the capacitive element C1-CSi and the capacitive elementCSi-C2 and the control electrode SG (DT) of the drive transistor DT toeach other. Accordingly, the line M3 performs a function of a chargepath which extends from another end of the switching element SW3 to thesemiconductor layer CSi and a voltage signal path which extends from thenode (contact hole) CH1 to the control electrode SG (DT) of the drivetransistor. The line M4 is formed as a voltage signal path which isprovided between the output side (also referred to as a source) of theswitching element SW1 and the upper electrode C1 of the capacitiveelement C1-CSi.

Since the current supply line PL is also included in the conductivelayer formed by the fourth photo pattern, with respect to the conductivematerial formed in the photolithography process using this mask, it ispreferable to reduce the resistance of such a conductive materialcompared to a conductive material which is formed in thephotolithography process using the mask of the second photo pattern. Forexample, it is recommendable to use aluminum or an alloy or silicidecontaining aluminum as the conductive material formed using the fourthphoto pattern.

In this embodiment, using this aluminum which constitutes the conductivematerial, the current supply line PL and the branch line PLB, the drainline DL and a group of lines M1, M2, M3, M4 are formed on the secondinsulation film. Further, via the contact holes formed by the thirdphoto pattern using the aluminum, the semiconductor layers CSi, Mg whichlie below the second insulation film, the electric current path whichreaches any one of the conducive layers C1, C2, SG (DT), the charge pathand the voltage signal path are also respectively formed. Accordingly,in the explanation of this embodiment described hereinafter, theabove-mentioned conductive layers PL, PLB, DL, M1, M2, M3, M4 which areformed by the photolithography process using the mask on which thefourth photo pattern is formed may be also indicated by the referencecharacters, AL, ALS.

FIG. 7 shows the fifth photo pattern as well as the sixth photo patternused for the formation of the pixel array shown in FIG. 2. Here, beforeperforming the photolithography process using the mask having the fifthphoto pattern, the third insulation film (the insulation film IC shownin FIG. 8 and FIG. 9) is formed on the conductive layers AL such as thecurrent supply line PL, the line M1 and the like using the fourth photopattern, and the contact holes Cont-ITO are formed in the region whichis positioned above the line M1. Any drawings which are relevant to thisprocess is omitted from this specification.

The fifth photo pattern has only the pattern indicated by a rectangularframe ITO shown in FIG. 7. Due to such a pattern, the transparentelectrode ITO is formed on the above-mentioned third insulation film ina strip shape and the portion of the transparent electrode ITO iselectrically connected with the line M1 through the contact holeCont-ITO. The transparent electrode ITO which is formed in thephotolithography process using the mask having the fifth photo patternis formed of an amorphous layer or a polycrystalline layer of aconductive oxide which allows light to path therethrough and istypically represented by an indium-tin oxide (also abbreviated as ITO)and an indium-zinc oxide (also abbreviated as IZO). In the organic ELlight emitting display device, it is necessary to form anelectro-luminescence material layer (included in the organic materiallayer OCT) which constitutes the light emitting portion such that theelectro-luminescence material layer has a uniform thickness andflatness. Further, it is required to expel a high temperature processwhich decomposes the organic material layer OCT from the manufacturingprocess. Under such circumstances, with respect to the above-mentionedconductive oxide such as the indium-tin-oxide or the like, even when thetemperature of heat treatment is suppressed at a low temperature, it ispossible to obtain a film with small surface roughness and hence, theconductive oxide is suitable for the organic EL light emitting displaydevice shown in this embodiment. After forming the transparent electrodeITO for every pixel region in the photolithography process using themask having the fifth photo pattern, a fourth insulation film which isformed on the bank BMP explained later is formed on an upper surface ofthe transparent electrode ITO and an upper surface of theabove-mentioned third insulation film on which the transparent electrodeITO is not formed.

The sixth photo pattern includes only a pattern indicated by anoctagonal frame BMP shown in FIG. 7. Due to such a constitution, anoctagonal opening is formed in the fourth insulation film which coversthe upper surfaces of the above-mentioned transparent electrode ITO andthe third insulation film thus completing a bank BMP. The bank BMP (thefourth insulation film) is formed of an organic film such as polyimideor an inorganic film such as SiO₂. The light emitting region of theorganic EL element is formed by supplying the organic material in asublimed state or as droplets to the transparent substrate ITO andhence, it is recommendable to form indents which separate the electriccurrent which flows into the organic material layer OCT (theelectro-luminescence material layer included in the organic materiallayer OCT) for every pixel. Accordingly, the bank BMP formed of aninsulation film which separates the light emitting region for everypixel is formed on the transparent electrode ITO. In the organic ELlight emitting display device of this embodiment, the bank BMP havingthe octagonal opening portion (indicated by the reference character OPNin FIG. 2) is overlapped to the periphery of the transparent electrodeITO and the center portion (corresponding to the light emitting region)of the transparent electrode ITO is exposed through the opening of thebank BMP.

In the organic EL light emitting display device according to thisembodiment, the above-mentioned fourth insulation film which constitutesthe bank BMP is formed of either an inorganic material such as SiO₂,SiN_(X) or the like and a black material. The bank BMP which is formedof the latter material is referred to as a black bank hereinafter. Thisblack bank BMP is formed of positive-type photosensitive blackpolyimide, for example. As this type of material, in this embodiment, aproduct JR 3120P made by Nitto Denko Corporation is exemplified. Sincethe organic material layer OCT is formed in the opening of the bank BMPas mentioned above, the light emitting region included in the organicmaterial layer OCT and the bank BMP are optically coupled. Accordingly,if the bank BMP is transparent or semitransparent with respect to lightfrom the organic material layer OCT, light from the organic EL elementLED formed on a certain pixel propagates into the inside of the bank BMPand there may be a case that the light leaks to another pixel which isarranged close to the pixel. This leaking of light between the pixels isrecognized as smear by a viewer. Although the bank (bank layer) BMPsurely separates the electric current which flows in the light emittingregion for every pixel and enhances the definition of the display imageof the organic EL light emitting display device, the bank (bank layer)BMP has the possibility that the image quality of the display image isextremely deteriorated due to light from the light emitting region inwhich the light propagates. Further, light having the intensity ofseveral hundred thousands luxs is irradiated from the light emittingregion formed on each pixel of the organic EL emitting display device.

To cope with the problem on leaking of light in the organic EL lightemitting display device which cannot be prevented by such a lightshielding structure similar to that of the conventional TFT type liquidcrystal display device, according to the present invention, in the pixelregion shown in the plan view, members which are included in the pixelcircuit are formed of a light shielding material. That is, as in thecase of the organic EL light emitting display device described in thisembodiment, respective upper electrodes C1, C2 of the capacitiveelements C1-CS1, CSi-C2 and the portion GLS of the scanning signal lineGL are arranged in the periphery of the light emitting region so as toobstruct leaking of light between the pixel. Further, according to thepresent invention, in the pixel region which is shown in the crosssectional views (see FIG. 8 and FIG. 9), the black bank BMP is arrangedclose to the light emitting region thus obstructing light propagatingfrom a side surface of the light emitting region to a main surface ofthe substrate (SGP in FIG. 8 and QGP in FIG. 9) through a group ofswitching elements. Here, in this specification, the above-mentionedlight shielding structure of the black bank BMP constitutes a novelstructure in the organic EL light emitting display device and isdisclosed as the separate invention from the light shielding structurewhich uses members included in the previously-mentioned pixel circuit.However, the light shielding structure which adopts both of them alsoconstitutes a novel structure.

FIG. 8 is the cross sectional view of the pixel region of the organic ELlight emitting display device according to the present invention whichis formed on the substrate SGP made of soda glass. When the soda glasssubstrate SGP is used as the TFT substrate, a silicon nitride layerSiN_(x) and a silicon oxide layer SiO₂ are sequentially laminated to thesubstrate SGP thus forming an insulation film IA. On portions of anupper surface of the insulation film IA on which the switching elementsSW1, SW2, SW3 and DT are formed, semiconductor channels FG are formedusing polycrystalline silicon (Poly-Si). The semiconductor channels FGare formed in the above-mentioned photolithography step which uses themask having the first photo pattern.

The upper surfaces of the semiconductor channels FG are, together withan upper surface of the insulation film IA on which the semiconductorchannels FG are not formed, covered with an insulation film GI made ofsilicon oxide SiO₂. The insulation film GI provides an insulationbetween the channel of the switching element and the control electrodewhich controls the conductive state of the channel and is also referredto as a gate insulation film. This insulation film GI may be formed ofsilicon nitride SiN_(X). On portions of an upper surface of theinsulation film GI on which the switching elements SW1, SW2, SW3 and DTare formed, respective control electrodes (conductive layers) SG areformed by a photolithography step which uses the above-mentioned maskhaving the second photo pattern. Further, although not shown in FIG. 8,the above-mentioned capacitive elements C1-CSi and CSi-C2 are alsoformed such that the insulation film GI is sandwiched between the lowerelectrode CSi which is formed together with the semiconductor channel FGand the upper electrodes C1, C2 which are formed together with thecontrol electrode SG.

The upper surface of the control electrode SG is, together with theupper surface of the insulation film GI on which the control electrodeSG is not formed, covered with an insulation film IB formed of siliconoxide SiO₂. On an upper surface of the insulation film IB, lines(conductive layers) AL, ALS which are connected to the switchingelements are formed by a photolithography step using the above-mentionedmask having the fourth photo pattern. Although two switching elementsshown in FIG. 8 respectively correspond to the drive transistor DT andthe switching element SW2 shown in FIG. 2, for facilitating thepreparation of the drawing, the switching element is depicted in adeformed shape. As shown in FIG. 8, the conductive layers AL, ALS areconnected to the upper surface of the semiconductor channel FG throughcontact holes Cont which penetrate the insulation film GI, IB.

On upper surfaces of the conductive layers AL, ALS and the insulationfilm IB, an insulation film IC formed of silicon oxide SiO₂ or siliconnitride SiN_(x) is formed. On the insulation film IC, a transparentelectrode ITO of the organic EL element is formed by a photolithographystep using a mask having the above-mentioned fifth photo pattern. Thetransparent electrode ITO is connected to the conductive layer ALSthrough a contact hole Cont-ITO which is formed by penetrating theinsulation film IC. The black bank BMP is formed such that the blackbank BMP covers portions of the insulation film IC and the transparentelectrode ITO. In the opening portion of the black bank BMP, an organicmaterial layer OCT including a light emitting region of the organic ELelement is formed. The organic material layer OCT is formed between thetransparent electrode ITO and the electrode CM and may include anelectron transfer layer and a hole transfer layer together with thelight emitting portion. Due to an electric current which flows betweenthe electrodes ITO and CM of the organic EL element, light is irradiatedfrom the light emitting region of the organic material layer OCT. Theorganic EL light emitting display element described in this embodimenthas an electrode CM side thereof covered with a member CG such as asealing glass or an end-sealing material and inert gas such as nitrogenis sealed in a space BG defined between the sealing member CG and theelectrode CM. This space BG may be sealed by a mold or the like which isused in a semiconductor process. Further, the upper surface of theelectrode CM may be covered with an insulation film in place of thesealing member BG.

Light from the organic material layer OCT arranged at the openingportion of the bank is irradiated toward the lower side (substrate SGPside) as indicated by two arrows in FIG. 8. Accordingly, an imagedisplayed by the organic EL light emitting display device is alwaysformed on a lower surface of the substrate SGP. When the light which isdeflected and irradiated sideward from the organic material layer OCT isdirectly irradiated to the semiconductor channel FG of the switchingelement, the image quality of an image displayed by the organic EL lightemitting display device driven by the switching element is degraded. Tocope with this problem, in the cross-sectional structure of the pixelregion shown in FIG. 8, the portion ALS of the line AL which isconnected to the switching element is extended to the opening portionside of the bank. In the structure shown in FIG. 8 which uses theportion ALS of the line AL as the light shielding member, the line M1and the branch line PLB of the current supply line shown in FIG. 1(A)and FIG. 6 are formed in a deformed shape. Due to the portion ALS ofthis line AL, an irradiation angle of the light from the organicmaterial layer OCT is restricted as indicated by a thin arrow in FIG. 8so that the light from the organic material layer OCT is not irradiatedto the semiconductor channel FG. As shown in FIG. 8, the opening portionof the bank BMP is formed in a tapered shape and hence, an end portionof the organic material layer OCT is overlapped to an oblique face whichborders the opening of the bank BMP. The portion of the organic materiallayer OCT which is inclined with respect to a main surface of thesubstrate SGP in this manner transmits the light in an unexpecteddirection. To shield such an unexpected light, the portion ALS of theline AL is formed such that the portion ALS is extended to the openingportion of the bank BMP. The present invention exhibits the advantageouseffects in the so-called bottom emission type organic EL light emittingdisplay device.

FIG. 9 is a cross-sectional view of the pixel region of the organic ELlight emitting display device according to the present invention whichis formed on a quartz substrate QGP. A point which makes thecross-sectional structure shown in FIG. 9 different from thecross-sectional structure shown in FIG. 8 lies in that the insulationfilm IA is not formed in the former structure. In case that the sodaglass substrate SGP is adopted, the insulation film IA is provided forprotecting the semiconductor channel FG from the impurities of the sodaglass substrate SGP. However, the probability that the impuritiespropagate from the quartz substrate QGP to the semiconductor channel FGis extremely small and hence, the insulation film IA is not necessary inthe organic EL light emitting display device which is formed on a mainsurface of the quartz substrate QGP. Here, except for the insulationfilm IA, the cross-sectional structure shown in FIG. 9 is substantiallyequal to that shown in FIG. 8. Also in the cross-sectional structureshown in FIG. 9, in the same manner as the cross-sectional structureshown in FIG. 8, the end portion of the bank and the portion ALS of theline AL are overlapped to each other and hence, it is possible toprevent the propagation of the light reflected on the end portion of thebank toward the semiconductor channel FG. Accordingly, in both of thecross-sectional structures shown in FIG. 8 and FIG. 9, it is possible toobtain large advantageous effect in the reduction of smear and theenhancement of contrast irrespective of the optical transmissivity ofthe bank material (for example, even when the bank is a transparentbank).

FIG. 10(a) to FIG. 10(c) show the cross-sectional structure of the pixelregion PIX which constitutes one of a plurality of pixels which arearranged in the pixel array shown in FIG. 2. FIG. 10(a) shows a crosssection of the portion of the pixel region PIX taken along a dashed lineA-A. In this portion, the conductive layer ALS of the drain line DL andthe capacitive element CSi-C2 are overlapped to each other and the bankBMP and the light emitting region OCT of the organic EL element abuteach other. In FIG. 10(a), a taper angle “a” made by the transparentelectrode ITO and the opening end portion (oblique surface) of the bankBMP formed on the transparent electrode ITO is held within 50 degrees.Here, the upper electrode C2 of the capacitive element CSi-C2 whichfunctions as a shield at the opening end portion of the bank BMP isspaced apart from the end portion of the opening of the bank BMP to anextent that light from the organic material layer OCT does not turnaround and reach another pixel region arranged close to the left side ofthe pixel region PIX.

FIG. 10(b) shows a cross section of the portion of the pixel region PIXtaken along a dashed line B-B and the contact hole Cont-PL is formed inthe portion. In FIG. 10(b), there is shown the conductive layer ALS ofthe current supply line PL which is bonded to the upper surface of theconductive layer C2 (portion projected from the capacitive elementCSi-C2) which constitutes the upper electrode of the capacitive elementCSi-C2 at the contact hole. In FIG. 10(b), a taper angle “b” made by thetransparent electrode ITO and the opening end portion (oblique surface)of the bank BMP formed on the transparent electrode ITO is about 57degrees. Here, the conductive layer C2 (the upper side electrode of thecapacitive element CSi-C2) which functions as a shield at the openingend portion of the bank BMP is spaced apart from the end portion of theopening of the bank BMP to an extent that light is not directlypropagated from a boundary between the opening of the bank BMP and theorganic material layer OCT to the channel regions of the switchingelements (SW1, SW2, SW3, DT) of the pixel arranged close to the pixelregion PIX.

FIG. 10(c) shows a cross section of the portion of the pixel region PIXtaken along a dashed line C-C, wherein the capacitive element C1-CSiwhich is arranged between the light emitting region (the organicmaterial layer OCT) and a group of switching element SW1, SW2, SW3, DTand the conductive layer ALS of the line M1 which is arranged above thecapacitive element C1-CSi and is bonded to the transparent electrode ITOare shown. The upper electrode C1 of the C1-CSi is disposed close to aboundary between the opening end portion of the bank BMP and the lightemitting region (the organic material layer OCT) of the organic ELelement and shields the switching element SW3 and the like from lightemitted from the organic material layer OCT. In FIG. 10(c), the upperelectrode C1 is extended to the left side and is expanded between theorganic material layer OCT and a group of switching elements thussufficiently performing the function of shielding respective channels ofa group of switching elements from light emitted from the organicmaterial layer OCT. In FIG. 10(c), a taper angle “c” made by thetransparent electrode ITO and the opening end portion (oblique surface)of the bank BMP formed on the transparent electrode ITO is held within50 degrees.

As has been explained in conjunction with FIG. 10(a) to FIG. 10(c), thetaper angle made by oblique surface of the opening of the bank BMP andthe main surface of the transparent electrode ITO depends on thearrangement of the end portion (portion which abuts the transparentelectrode ITO) of the bank BMP and the shielding layer (light shieldingmember) exemplified as the upper electrodes C1, C2 of the capacitiveelement C1-CSi and the capacitive element CSi-C2. The positionalrelationship between the end portion of the bank BMP and the end portionof the shielding layer is explained in conjunction with models shown inFIG. 11(a) and FIG. 11(b).

FIG. 11(a) shows the bank which is projected outwardly from the endportion of the shielding layer, wherein the position of an edge of thebank is determined by an axis X of coordinates which set the end portionof the shielding layer as a 0 point (a base point). The position X ofthe edge of the bank formed outside the shielding layer is expressed bya value having plus (+). That is, the position of the edge of the bankfalls within a range of X>0. The greater the distance that the bank isprojected from the end portion of the shielding layer (the greater thedistance that the edge of the bank extends toward the right side in FIG.11(a)), the value of X is increased.

FIG. 11(b) shows the bank which is retracted inwardly from the endportion of the shielding layer, wherein the position of an edge of thebank is positioned on the shielding layer. Also in FIG. 11(b), theposition of the edge of the bank is determined by the above-mentionedaxis X of coordinates which set the end portion of the shielding layeras the 0 point (a base point). The position X is expressed by a valuehaving minus (−). That is, the position of the edge of the bank shown inFIG. 11(b) falls within a region of X<0. Further, the greater thedistance that the edge of the bank extends toward the left side in FIG.11(b), the value of X is decreased.

The inventors have investigated the change of taper angle made by theoblique surface of the bank opening and the main surface of thetransparent electrode (main surface of the substrate) and the change ofcontrast of an image displayed on the pixel array with respect to theabove-mentioned distance X (μm) between the end portion of the shieldinglayer and the edge of the bank defined along the axis X of coordinatesand the result of the investigation is shown in FIG. 12. In FIG. 12,black dots indicate the above-mentioned taper angle and white dotsindicate the display contrast of the pixel array respectively. The taperangle θ of the bank is increased in the vicinity of X=0 where the edgeof the bank is overlapped to the end portion of the shielding layer.When the taper angle θ of the bank approaches 90°, the electrode(electrode CM shown in FIG. 8 and FIG. 9) which is formed such that theelectrode extends from the upper surface of the bank to the inside ofthe opening of the bank is liable to be cut due to a stepped portionformed in the edge of the bank opening.

When the electrode is cut in such manner at the stepped portion formedin the pixel, such an impurity as moisture or oxygen easily gets intothe organic material layer from outside through a break of the electrodeand deteriorates reliability of the organic EL element. As FIG. 12shows, when the above-mentioned distance X lies in a range of ±1 μm, thetaper angle θ of the bank becomes larger than c.a. 65 so that thestepped portion of the electrode can be easily formed. Such inclinationof the electrode to form the stepped portion thereof in accordance withthe taper angle θ of the bank is basically common to a bank formed of aninorganic material.

On the other hand, as the taper angle θ of the bank approaches closer to90°, leaking of light from the light emitting layer of the neighboringpixel is hardly generated so that the contrast of the image displayed onthe pixel array is enhanced. The contrast ratio which is one of theindices for evaluating the image quality exhibits the tendency that itis generally worsened when the distance X is increased. This tendency isattributed to a phenomenon that when the distance X is increased, thelight shielding of the channel region of the switching element becomesinsufficient. From a practical point of view, the positionalrelationship among the light emitting layer, the shielding layer and thechannel region of the transistor is important for improving the contrastratio. In this respect, as described in the above-mentioned embodiment,it is preferable to arrange the shielding layer to a position where atleast light from the light emitting layer in the vicinity of the edge ofthe bank layer is not directly irradiated to the channel region.Further, the factor that the contrast ratio is largely enhanced when thedistance X is made small is irrelevant to the taper angle of the edge ofthe bank and rather lies in that the reflection light at the edge of thebank is obstructed and is not irradiated from the pixel array.

To arrange the above-mentioned principles, the present invention can begrasped as a single form or a combination of following constitutions.

(1) The shielding layer is arranged at the position where light from thelight emitting layer of the pixel on which the shielding layer is formedis not directly irradiated to the channel region of the switchingelement which controls the pixel or another pixel which is disposedclose to the pixel.

(2) At least one of the scanning signal line, the data signal line(drain line) and the current supply line which are arranged between thepixels arranged close to each other is configured to have a width whichcan prevent light from the light emitting layers of respective pixelsfrom being reflected and leaked to the neighboring pixel or thearrangement or the interval of these components are adjusted so thatthey function as a shielding layer.

(3) In a plan view of the pixel, when the boundary between the edge ofthe bank and the light emitting layer is projected from the end portionof the shielding layer (the above-mentioned case in which X is set toX>0), to reduce leaking of light from the light emitting layer of theneighboring pixel, in addition to the above-mentioned constitution (1)or the above-mentioned constitution (2), the bank layer per se isblackened or the bank layer is formed of an inorganic film (SiN_(x)and/or SiO₂) which permits film thickness thereof to be thinned. Withrespect to the latter bank layer, it is desirable to make the bank layerthin to prevent the rupture of the electrode layer formed thereon,wherein it is preferable to set the film thickness to a value whichfalls within a range of several tens nm to several hundreds nm, forexample.

(4) The end portion of the shielding layer in the planar structure ofthe pixel is projected to the light emitting layer side from theboundary between the edge of the bank layer and the light emitting layer(the above-mentioned state in which X is set to X<0). In this case, thebank may be transparent or blackened, and may also be formed of aninorganic material.

FIG. 13 shows the cross-sectional structure of the pixel of the organicEL light emitting display device to which the present invention isapplied. The materials and the film thicknesses of respective thin filmsindicated in the cross-sectional view can be suitably changed. Therelationship among the distance X (μm) between the end portion of theshielding layer and the edge of the bank shown in FIG. 12, the taperangle of the bank opening and the contrast of image is obtained bychanging the shapes of the line which supplies the electric currentoutputted from the channel FG of the switching element to thetransparent electrode ITO and the opening of the bank BMP in the organicEL light emitting display device having the cross-sectional structureshown in FIG. 13. In the cross-sectional structure shown in FIG. 13,although the film thickness of the bank BMP is set to 2000 nm, the filmthickness differs corresponding to the material of the bank. In thecross-sectional structure shown in FIG. 13, on the main surface of thequartz substrate QGP, the channel FG made of polycrystalline silicon,the insulation film GI, the control electrode (gate) SG made oftitanium-tungsten alloy (TiW), the insulation film IB, theabove-mentioned line (conductive layer) having three-layered structureof a cap layer made of titanium-tungsten alloy (TiW)/aluminum (Al)/abarrier layer made of titanium-tungsten alloy (TiW), the insulationlayer IS, SiN, the transparent electrode ITO, the bank BMP, the organicmaterial film OL including the light emitting region, and the electrodelayer CM are sequentially formed.

FIG. 14 shows display images in an experiment in which the contrast ofthe organic EL light emitting display device to which the presentinvention is applied and the contrast of the conventional organic ELlight emitting display device are compared. In the experiment,respective display screens (pixel arrays) of a pixel array to which thepresent invention is applied and a pixel array to which the presentinvention is not applied are divided into 9 sections. Then, thecomparison of the contrast under the ANSI Standard (the Standard definedby American National Standard Institute) in which black sections andwhite sections are alternately displayed (hereinafter referred to as“first comparison”) and the comparison of contrast when respective wholedisplay screens are displayed in black and white respectively(hereinafter referred to as “second comparison”) are performed.

In the first comparison, the luminance A (ANSI white) of the center ofthe pixel array when the center of the pixel array is displayed in whiteand the luminance B (ANSI black) of the center of the pixel array whenthe center of the pixel array is displayed in black are measured and theratio of luminance is calculated as the contrast ratio. With respect tothe conventional pixel array to which the present invention is notapplied, the luminance A is 180 cd/m² and the luminance B is 2.0 cd/m²and hence, the contrast ratio in the center portion of the pixel arrayis calculated as 90:1. To the contrary, with respect to the pixel arrayto which the present invention is applied, the luminance A is 200 cd/m²and the luminance B is 0.1 cd/m² and hence, the contrast ratio in thecenter portion of the pixel array is calculated as 2000:1.

In the second comparison, the luminance C of the center of the pixelarray when the whole pixel array is displayed in white and the luminanceD of the center of the pixel array when the whole pixel array isdisplayed in black are measured and the ratio of luminance is calculatedas the contrast ratio. With respect to the conventional pixel array towhich the present invention is not applied, the luminance C is 180 cd/m²and the luminance D is 0.12 cd/m² and hence, the contrast ratio in thecenter portion of the pixel array is calculated as 1500:1. To thecontrary, with respect to the pixel array to which the present inventionis applied, the luminance C is 200 cd/m² and the luminance D is 0.1cd/m² and hence, the contrast ratio in the center portion of the pixelarray is calculated as 2000:1.

In this manner, in the conventional organic EL light emitting displaydevice which does not adopt the light shielding structure of the presentinvention, the contrast ratio which is calculated by displaying thewhole screen in white and in black is 1500:1 and the so-called ANSIcontrast ratio which is calculated when the white-and-black checkeredpattern is displayed on the screen in an inverted manner is 90:1. Asdescribed above, in the screen which displays the white-and-blackcheckered pattern, the luminance B of the pixel to be displayed in blackis not sufficiently lowered. Further, the contrast ratio is influencedby the display image depending on the display image.

To the contrary, with respect to the organic EL light emitting displaydevice according to the present invention, the contrast ratio is largelyenhanced to 2000:1 in both cases and the contrast ratio is notinfluenced by the display image. Further, in the screen which displaysthe white-and-black checkered pattern, the luminance B of the pixel tobe displayed in black is sufficiently lowered so that a profile of anobject to be displayed can be sharply displayed. Accordingly, in theorganic EL light emitting display device according to the presentinvention, it is possible to remarkably enhance the image quality of thedisplay image compared to the image quality of the display image of theconventional organic EL light emitting display device.

FIG. 15 is a view showing steps of the manufacturing process of theorganic EL light emitting display device to which the present inventionis applied while focusing on the portion (TFT portion) where the drivetransistor is mounted. Although the thin film transistor having aso-called top gate structure which mounts the control electrode on thechannel as the drive transistor is used in this embodiment, even whenthe thin film transistor having a bottom gate structure is adopted inplace of the thin film transistor having the top gate structure, themanufacturing process thereof is substantially equal to that of the thinfilm transistor having the top gate structure. The steps of themanufacturing process are explained hereinafter in the order of (1) to(10) in conformity with the respective numbers of cross-sectional views.

(1) The semiconductor layer FG made of amorphous silicon is formed onthe glass substrate SUB by patterning and the semiconductor layer FG isformed into the polycrystalline silicon layer by applying laserannealing.

(2) The first insulation layer IA is formed on the semiconductor layerFG made of polycrystalline silicon.

(3) The conductive thin film made of titanium (Ti), tungsten (W) or thelike is applied to the first insulation layer GT and the conductive thinfilm is subjected to patterning on the upper portion of thesemiconductor layer FG thus forming the gate electrode GL.

(4) The second insulation layer IB is formed such that the secondinsulation layer IB covers the gate electrode GL and the firstinsulation layer GI and the contact holes are formed in necessaryplaces.

(5) The aluminum line which constitutes the source electrode AL isformed on the second insulation layer IB (When necessary, this aluminumthin film is sandwiched by titanium (Ti) or tungsten (W) or the like.)

(6) The third insulation layer IC which covers the above-mentionedaluminum line AL is formed.

(7) The protective film PSV made of silicon nitride (SiN) or the like isformed on the third insulation layer IC. The contact hole whichpenetrates the protective film PSV and the third insulation layer IC andreaches the source electrode FG is formed.

(8) The thin film made of indium-tin-oxide (ITO) is applied to theprotective film PSV thus forming the electrode ITO. In this manner, thefirst electrode layer ITO of the organic EL element is formed. A portionof the first electrode layer ITO is connected to the source electrode ALthrough the contact hole.

(9) The bank BMP for insulating the organic light emitting layer fromthe end portion of the first electrode ITO is formed. The opening isformed in the bank BMP at a position corresponding to the light emittingregion. The bank BMP is formed of black polyimide having fluidity. Theinner wall of the opening of the bank BMP which is formed in the lightemitting region is formed in a tapered shape toward an upper surface ofthe first electrode layer ITO due to heat applied at the time of formingthe pattern.

(10) The organic light emitting layer OCT is applied to the opening ofthe bank BMP in the light emitting region. The organic light emittinglayer OCT is applied using a technique such as mask printing, an ink jetor the like.

(11) The metal layer is formed such that the metal layer covers theorganic light emitting layer OCT thus forming the second electrode layerCM of the organic EL element.

After performing the above-mentioned steps, the second electrode layerCM side is sealed with the sealing can or a suitable member made ofglass, ceramics or the like thus completing the display device as amodule.

FIG. 16 shows the arrangement of a group of lines of the organic ELlight emitting display device to which the present invention is applied.The organic EL light emitting display device of the present invention isconfigured such that a display part DIP (region surrounded by a dottedline in FIG. 16) is formed by arranging a plurality of drain lines DLand a plurality of scanning signal lines (gate lines) GL in a matrixarray on the quartz substrate QGP, and a data driving circuit DDR, ascanning driving circuit DDG and a current supply circuit PW arearranged in the periphery of the display part DIP.

The data driving circuit DDR is provided with a complementary circuitwhich includes TFTs (thin film transistors) having N-type channels andTFTs having P-type channels, a shifter register circuit which includesonly TFTs having N-type channels or only TFTs having P-type channels, alevel shifter circuit, an analogue switch circuit and the like. Here,the current supply circuit PW has only a bus line thereof formed on thequartz substrate QGP and an electric current may be supplied to the busline from an external current source.

In the organic EL light emitting display device shown in FIG. 16,capacitors (not shown in the drawing) which adjust the operation of thedrive transistors of respective pixels are arranged in the display partDIP and the current supply line PL to which one ends of respectivecapacitors are connected is provided for every column of pixels. Anotherends of the above-mentioned capacitors are connected to a common currentsupply line PLC which is provided for every row of pixels. The currentsupply lines PL are connected to an external common potential sourcethrough a terminal PLT of a common potential bus line PLA.

FIG. 17 shows a circuit constitution of the organic EL light emittingdisplay device to which the present invention is applied. As shown inFIG. 17, in each pixel PX which is surrounded by the data lines DL andthe gate lines GL, the switching element (control transistor) SW1, thecurrent supply transistor (drive transistor) DT, the capacitor C and theorganic EL element LED are arranged. The switching element SW1 has thecontrol electrode (gate) thereof connected to the gate line GL and oneend of the channel (drain) connected to the data line DL. The gate ofthe current supply transistor DT is connected to the other end (source)of the switching element SW1 and one electrode (+ pole) of the capacitorC is connected to the node. The current supply transistor DT has one end(drain) of the channel thereof connected to the current supply line PLand another end (source) thereof connected to an anode of the organic ELelement ELD. The data lines DL are driven by the data driving circuitDDR and the scanning signal lines (gate lines) GL are driven by thescanning driving circuit DDG. Further, the current supply lines PL areconnected to the current supply circuit PW through the common potentialsupply bus line PLA.

In FIG. 17, when one pixel PX is selected through the scanning signalline GL and the switching element (control transistor) SW1 is turned on,the image signal supplied from the data line DL is stored in thecapacitor C. Thereafter, at a point of time that the switching elementSW1 is turned off, the current supply transistor DT is turned on so thatthe electric current flows into the organic EL element LED from thecurrent supply line PL substantially for one frame period. The electriccurrent which flows into the organic EL element LED is adjusted by thecurrent supply transistor DT and the voltage corresponding to the chargestored in the capacitor C is applied to the gate of the current supplytransistor DT. Accordingly, the emitting of light of the pixel iscontrolled. Although not shown in FIG. 17, the operation level of thecapacitor C may be controlled based on the potential of the controlsignal lines CL1, CL2 shown in FIG. 1(A).

In the pixel structure shown in FIG. 1(A), since the control signallines CL1, CL2 are formed such that these lines penetrate the portionsof the pixel region, the area of the light emitting region isrestricted. However, the provision of the control signal lines CL1, CL2brings about an advantage that the operation of a plurality of currentsupply transistors DT arranged within the display screen can be adjustedso that the image can be produced on the display screen without beinginfluenced by the irregularities of the characteristics of these currentsupply transistors DT.

FIG. 18 shows a so-called pixel circuit which is provided to one of aplurality of pixels PX shown in the above-mentioned FIG. 17. The pixelshown in FIG. 18 is surrounded by the drain line (data line) DL, thescanning signal lines GL(n+1), GL(n) and the current supply line PL.

In the pixel circuit shown in FIG. 18, one terminal of the capacitor Cwhich is connected to the node between the one end (source) of thechannel of the switching element (control transistor) SW1 and thecontrol electrode (gate) of the current supply transistor DT constitutesa + pole and another end thereof which is connected to the scanningsignal line GL(n) constitutes a (−) pole.

The organic EL element (organic light emitting element) LED has aso-called PIN-type diode structure in which an organic light emittinglayer (not shown in the drawing) is interposed between the firstelectrode layer ITO (anode) and the second electrode layer (cathode) CM.Here, the first electrode layer ITO is connected to one end (source) ofthe channel of the current supply transistor DT and the second electrodelayer CM is formed not only in the pixel shown in FIG. 18 but also inthe whole pixel array region shown in FIG. 17 in which a plurality ofpixels are arranged.

Here, a quantity of charge which corresponds to the image signal (alsoreferred to as “video signal” or “data signal”) supplied to thecapacitor C from the drain line DL through the switching element SW1 isheld. Accordingly, the charge held in the capacitor C also correspondsto the gray scale to be displayed by the pixel PX and hence, bycontrolling the current supply transistor (drive transistor) DT usingthe control voltage corresponding to the quantity of charge, theelectric current corresponding to the gray scale flows into the organiclight emitting element LED.

The organic light emitting element LED emits light with luminancesubstantially proportional to a quantity of current supplied to theorganic light emitting element LED and with color corresponding to theorganic light emitting material (electroluminescence material) whichconstitutes a light emitting layer formed on the organic light emittingelement. In the organic EL light emitting display device which performsthe color display, the organic light emitting layer materials which areused in the light emitting layer are changed corresponding to respectivepixels of red, green and blue in many cases. Further, it may be possibleto display the color image using the organic EL light emitting displaydevice in which the light emitting layers of respective pixels areformed using the organic light emitting layer materials which irradiateso-called white light and these light emitting layers are combined withcolor filters which are similar to those used in the liquid crystaldisplay device.

In all of the above-mentioned organic EL light emitting display devices,the video signals (data signals) can be transmitted in an analoguequantity or a time-division digital quantity. Further, it may bepossible to combine an area gray-scale method which divides the lightemitting area of respective pixels of red, green and blue to the grayscale control of the organic EL light emitting display device.

According to the present invention, in the organic EL light emittingdisplay device. which performs the image display by the active matrixdriving (TFT driving), it is possible to prevent the degradation ofimage quality and the occurrence of the smear. Further, the contrastratio and the luminance of the display image can be enhanced.Accordingly, it is possible to obtain the organic EL light emittingdisplay device which can perform the high quality image display.

1. An organic EL light emitting display device comprising: a substratehaving a main surface; a plurality of pixels arranged two-dimensionallyon the main surface of the substrate; a plurality of scanning signallines arranged in parallel in the first direction on the main surface ofthe substrate; a plurality of data signal lines arranged in parallel inthe second direction which intersects the first direction on the mainsurface of the substrate; and a plurality of current supply linesarranged on the main surface of the substrate; wherein each one of theplurality of pixels comprises: a plurality of active elements; andwherein an organic EL element which emits light in response to thesupply of the current which is adjusted by at least two of the activeelements, wherein said at lest two active elements connect to themselvesin series, wherein each gate of said at lest two active elements connectto one of the plurality of scanning signal line or comprise one of theplurality of scanning signal line, wherein gates of said at lest twoactive elements extend in different directions from one another.
 2. Anorganic EL light emitting display device according to claim 1, whereintwo gates of said at lest two active elements extend in perpendiculardirection to each other.
 3. An organic EL light emitting display deviceaccording to claim 2, wherein one of the two gates extends in the firstdirection, the another gate extends in the second direction.
 4. Anorganic EL light emitting display device comprising: a substrate havinga main surface; a plurality of pixels arranged two-dimensionally on themain surface of the substrate; a plurality of scanning signal linesarranged in parallel in the first direction on the main surface of thesubstrate; a plurality of data signal lines arranged in parallel in thesecond direction which intersects the first direction on the mainsurface of the substrate; and a plurality of current supply linesarranged on the main surface of the substrate; wherein each one of theplurality of pixels comprises: a plurality of active elements; andwherein an organic EL element which emits light in response to thesupply of the current which is adjusted by at least two of the activeelements, wherein said at lest two active elements connect to themselvesin series, wherein crystallized silicon of said at least two activeelements connect themselves each other, wherein silicon bends betweentwo active elements.
 5. An organic EL light emitting display deviceaccording to claim 4, wherein the crystallized silicon bendsperpendicularly between two active elements.
 6. An organic EL lightemitting display device according to claim 5, wherein the crystallizedsilicon bends from the second direction to the first direction.